The present invention relates to a porous resin film having excellent aqueous liquid absorbency and ink absorbency. The invention also relates to a recording medium which exhibits good ink jet recording properties and which allows the formation of a fine image.
A film-based synthetic paper having excellent water resistance comprises a resin as a main component and has heretofore been mainly used for offset printing or seal printing using oil-based or UV curing ink, sublimation, or melt type heat transfer, etc. As the film-based synthetic paper has found more applications, however, there has been a growing demand for printing methods using an aqueous ink and aqueous paste for environmental protection purposes. To this end, synthetic paper having good absorption of aqueous ink, aqueous paste, or water, which acts as a solvent therefor, would be desirable.
The recent progress of multimedia techniques means that ink jet process printers have become popular for use in both business or consumer applications. The ink jet process printer can be easily provided in the form of a multi-color display, and it can easily provide a large image. Thus, it desirably reduces the printing cost. In particular, ink jet printers using an aqueous ink, which has fewer environmental or safety problems as compared with oil-based ink, have become popular recently.
The ink jet printer has been widely used to obtain a hard copy with characters as well as images. Therefore, the printed image must be finer. The image fineness depends on the dryability of the ink printed on the recording medium. For example, when repeated printing is made on a plurality of recording medium sheets, other sheets of recording medium are often imposed on the printed recording medium. In this case, if the printed recording medium sheet has absorbed the ink insufficiently, the ink can transfer to the preceding recording medium sheet, causing image stain.
In order to enhance the fineness of image, a method has been widely employed which comprises coating an ink-receptive material that contains a hydrophilic resin or inorganic finely divided powder onto a recording medium such as plastic film or paper (Japanese Patent Laid-Open No. 1991-82589, Japanese Patent Laid-Open No. 1997-216456). A recording medium for ink jet recording having an ink-receptive layer mainly composed of a hydrophilic resin formed by heat lamination or extrusion lamination has also been proposed (Japanese Patent Laid-Open No. 1996-12871, Japanese Patent Laid-Open No. 1997-1920, Japanese Patent LaidOpen No. 1997-314983). However, the recording media formed by these methods have the disadvantage in that when the ejected amount of ink is great, the media cannot absorb the ink sufficiently, which requires that the thickness of the coat layer be increased, and which requires a plurality of coating steps.
An aim of the invention is to solve the problems of the conventional techniques.
In other words, an aim of the invention is to provide a porous resin film having good water absorption from aqueous inks or aqueous pastes and a recording medium which can absorb ink without density unevenness even if solid printing is carried out in which the ejected amount of ink is great in ink jet recording. Another aim of the invention is to provide a porous resin film constituting such a recording medium having excellent properties.